The present invention relates generally to the manufacture of rubber tires for wheeled vehicles, and more particularly, to a method and apparatus for applying a separately formed strip of tread stock to a previously assembled green tire carcass or to a belt package for subsequent application to a green tire carcass.
In manufacturing tires, the assembly of tire elements is generally completed when a separately formed strip or band of tread stock is attached to a green tire carcass, the tread stock being applied either individually or as a sub-assembly consisting of the belts and the tread stock. The tread stock is typically produced by extruding a continuous strip or band of uncured rubber, the extrusion having a cross-sectional shape that is generally hat-like, in that it includes a relatively massive central portion with thin extremities extending outwardly on either side at the lowermost edge of the stock. The strip or band is cut to suitable lengths for subsequent assembly on a green tire carcass or belt package.
The dimensional uniformity of any extruded shape is subject to many process variables. Thus, the thin outer extremities of the tread stock are susceptible to dimensional variation to such an extent that the extremities are generally not suitable as reference or guide points for handling and orienting the tread stock during its assembly to the carcass or the belt package. Because the central, more massive portion of the stock extrusion is dimensionally more uniform, tire manufacturers heretofore have generally focused attention on centrally locating the massive portion of the tread stock on the belt package or green tire carcass, with a lesser regard given to the positioning of the thin outer extremities.
In view of the foregoing, tire building machines and the tread stock servicers utilized therein for delivering stock are typically disigned to permit the building machine operator, through personal skill and substantial hand manipulation, to control and adjust the positioning of the tread stock as it is merged with and assembled to the belt package or green tire carcass.
To assist the machine operator in the orientation of the tread stock, a number of complex reference guide means have been developed. For example, U.S. Pat. No. 3,923,390, issued Dec. 2, 1975 to Susko, projects reference lines of light onto the surface of the belt and tread stock package being assembled. The projected lines are generally positioned to coincide with the rounded shoulder areas of the tread stock extrusion. A second example is disclosed in U.S. Pat. No. 3,026,230, issued Mar. 20, 1962 to Nebout.
As a result of these approaches, present tread stock servicer apparatus is generally configured so that the stock is oriented with the outermose surface (into which the tread will later be formed) in an upward position. The tread stock must therefore be delivered to the vicinity of the upper portion of the building drum supporting the belts or the green tire carcass, so that the tire building machine operator can visually observe the progress of tread stock application. When necessary, the operator may then utilize hand manipulation to control or adjust the positioning of the stock at the point where it merges with and is applied to the belts or green tire carcass.
The tread stock is delivered onto the belts along a line tangent to the circumference of the drum on which the building operation is performed. However, the foregoing requirements necessitate that the delivery end structure of the tread servicer be oriented within the angle of tangency between the stock and the building drum. Since the delivery end must have finite dimensions, it is physically impossible to have the tread stock servicer support and guide the tread stock at the exact point where the stock meets and is applied to the belts or green tire carcass carried on the drum, the point of greatest criticality in stock orientation.
Applying the tread stock to the belts or green tire carcass in other than a precisely centered manner can result, after the tread stock is assembled onto the green tire carcass, in a non-uniform displacement of rubber during the shaping stage of the curing process. This situation can result in a non-uniform tire. For example, consider a radial ply carcass on which the belts had been properly aligned and assembled. If the tread stock is applied either off center or in a crooked or wobbly manner, the unsymmetric or non-uniform lateral displacement of tread stock material may, during the shaping or curing process, result in a similar but opposite lateral displacement of one or more of the underlying belts. The presence of such laterally displaced belts in the finished, cured tire could adversely affect the tire's operating characteristics, and upon final inspection, such tires are discarded.
What is needed, therefore, is a tread stock servicer for a tire building machine that easily and reliably orients and positions the tread stock as it is brought into contact with the belts or green tire carcass positioned on the building drum. Such a servicer should reduce the skill and manipulation required on the part of the building machine operator, and shoul result in a higher degree of uniformity and symmetry in the application of the tread stock. In achieving these functions, such a servicer should support the tread stock as close as possible to the actual point of application of the stock to the building drum.